Abstract

The zinc-lead deposit described is located on Calumet Island, Quebec, 53 miles northwest of Ottawa. The complex ores resemble those of Edwards, New York, and Montauban, Quebec, and other Grenville deposits. They occur in moderately inclined Grenville metamorphic rocks, including crystalline limestone, amphibolite, amphibolite-gneisses, quartzitic (rusty-weathering) gneisses, and various granitized gneisses (migmatites). These represent argillaceous and calcareous sediments, contact metamorphosed and injected by a granitic magma of relatively high fluidity.

The sulphide minerals comprise pyrite, sphalerite, pyrrhotite, galena, tetrahedrite, chalcopyrite, and marcasite, deposited in the order named. The sulphides form lean disseminations in all of the rock types in the ore zones, and lenticular masses largely deposited in carbonate and contact metamorphic rocks. They replace carbonate, quartz, and all silicates except serpentine. The association of the ore minerals with quartz and contact silicates indicates that they accompanied the same agents that produced silicatization and silicification. The association of sulphides with late-stage processes in pegmatitelike material is evidence that they formed a phase of the pegmatitic or volatile-rich granite magma. This “pegmatitic” material is considered to have been responsible for the contact metamorphism and migmatization as well.

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